Electric actuators such as motors and solenoids have been widely used for conversion of electric signals to mechanical motions or hydraulic pressure as various control targets are electrically controlled. It is essential to control a current with high accuracy to sophisticate the electric actuators. In recent years, digital feedback control has been generally used for high-accuracy current control.
To execute digital feedback control of a current, it is necessary to acquire a digital value ioutd of a load current value Iout to be controlled. For this purpose, an output Vout of a current-to-voltage conversion circuit is converted into a digital value by an AD converter. Then, a relative digital value Voutd(=Vout/Vref) with a reference voltage Vref of the AD converter is acquired. Next, the output Voutd of the AD converter is corrected according to input and output characteristics of a current detection circuit that includes the current-to-voltage conversion circuit and the AD converter, thereby acquiring the digital value Ioutd of a current.
Although the current detection circuit has a variety of configurations, it is preferable that the input and output characteristics of the current detection circuit be linear from the perspective of simplifying a control algorithm. In this case, the current digital value Ioutd can be calculated using a gain a and an offset b as expressed by Equation (1).Ioutd=a·Voutd+b  (1)
When the current value is measured according to Equation (1), it is important how the gain a and the offset b match with actual characteristics of the current detection circuit with high accuracy in improving the accuracy of current measurement.
There is a great need to not only provide the high-accuracy current control but also to downsize a control device and reduce the price. Such need is met by incorporating a current detection circuit in an IC chip. To incorporate the current detection circuit in the IC chip, an IC chip that incorporates a resistor for current detection is known (refer to, for example, Patent Documents 1 and 2).